Two main types of hearing protectors are hearing protectors with ear cups and hearing protectors with ear plugs. Ear cups are intended to be positioned over the ears of a wearer and are usually secured by a headband, which runs partly around the wearer's head and which interconnects the hearing protectors. Ear plugs are intended to be positioned in the auditory canal and may also be secured by a corresponding headband.
Traditional hearing protectors comprise a sound-attenuating material, a sound absorber, which separates the inner parts of the ear from the surroundings. The purpose of the sound absorber is to prevent harmful noise from reaching the inner parts of the ear, for example the eardrum. Hearing protectors of this kind are called passive, since they attenuate all ambient sounds to the same degree over time.
In addition, more modern hearing protectors may comprise electronic circuitry that picks up ambient sounds through a microphone, converts them to appropriate levels and/or filters out the desired sound content and plays it back to the user by means of a speaker contained in the hearing protector. Hearing protectors of this kind are called active hearing protectors, because they contain, contrary to passive hearing protectors, active components.
Accordingly, a conversion of the sound occurs in active hearing protectors: first, the sound signal picked up by the microphone is converted to an electric signal for further signal processing, and then a sound signal is reproduced for the purpose of playing it back to the user through a speaker facing the user's ear.
One type of active hearing protector is a level-dependent hearing protector, which comprises an electronic circuit designed to adapt the sound pressure level. Such hearing protectors protect the user, for instance, by filtering out impulse noise, such as gunshots, from the surroundings, and/or by continuously adapting all ambient sound received to an appropriate level before it is reproduced to the user.
Active hearing protectors may be essential to allow communication in noisy environments and/or environments where the noise levels vary considerably, or where high impulse sounds might cause hearing damage. In this context, ‘communication’ may mean, for instance, that a person wearing a hearing protector needs to hear ambient sounds, such as machine sounds or speech, while being protected from harmful noise levels. Active hearing protectors featuring level adaptation are used, for example, in connection with airport operations and hunting.
In many applications either ear cups or ear plugs are used. However, in particularly noisy environments, such as in a helicopter or a tank, it may be advantageous to use both ear plugs and ear cups at the same time.
In these situations, where an active hearing protector is desirable, it is common to use either active ear plugs and passive ear cups or the opposite. Another alternative is to use double active hearing protectors. This implies, however, several conversions of the sound signal and, thus, increased distortion of the reproduced sound.
Using an active cup over a passive plug or an active plug inside a passive cup means that the user will have problems communicating with his surroundings. This is because all sounds, also the desired sounds, are attenuated by the passive protector to a level that makes communication more difficult or even impossible. If, for example, the user wears active ear cups in order to obtain satisfactory monitoring of ambient sounds, and supplements the protection with ear plugs, the level-adapted sound reproduced by the active cups will be further attenuated by the plugs to an extent where it is difficult to make out what is being said.
There is thus a need for an active hearing protector, which can offer sufficient noise attenuation in particularly noisy environments, while providing satisfactory sound quality for sounds reproduced by means of the active protection.